Enclosure defined

A weather-protected Type II machine shall have, in addition to the enclosure defined for a weather-protected Type I machine, its ventilating passages at both intake and discharge so arranged that high-velocity air and air-borne particles blown into the machine by... 

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

These have only a historical significance, in the light of better defined enclosures now available. They are briefly defined here ... 

Locations falling within this category can employ motors that are more economical than the other types discussed above. lEC 60079-14 has defined the basic requirements for such enclosures which are obviously less stringent than the others. In addition to maintaining specified creepages and clearances between the rotating and the stationary parts, the following are the two main requirements specified for such enclosures ... 

We have defined the various types of enclosures adopted by various manufacturers to suit different locations and environmental conditions in Tables 1.10 and 1.11. Here we briefly discuss methods for testing these enclosures to check their compliance with defined requirements. 

The types and degrees of enclosure protection are generally the same as defined for motors in Section 1.15, Tables... 

The continuous current rating of a bus system can be defined by the current at which a steady-state thermal condition can be reached. It is a balance between the enclosure and the conductor s heat gain and heat loss. If this temperature is more than the permissible steady-state thermal limit it must be reduced to the desired level by increasing the size of the conductor or the enclosure or both, or by adopting forced cooling. Otherwise the rating of the bus system will have to be reduced accordingly. 

Understanding of the technological process and identification of subprocesses are essential for proper ventilation design, especially when designing process ventilation but also in enclosure air technology. The purpose of process description is to identify possible emission sources, occupational areas, the effects of environmental parameters on production, needs for enclosure and ventilation equipment, etc. One purpose is to divide the process into parts such that their inputs and outputs (e.g., process, piping and duct connections, electricity, exposure) to environment can be defined. Parts here can he different departments, and inside them, subprocesses. See Fig. 3.4. 

Different protection factors have been defined. One method is to define it as the ratio of the concentration of a contaminant in the exhaust duct (CJ to the concentration in the breathing zone (C[,) of a person standing in front of the enclosure, for example, a laboratory fume hood ... 

Protection factors based on the ratio of the breathing zone concentration to the concentration inside the enclosure have been defined. Without complete mixing of air inside the enclosure, considerable variations in the concentration are expected. The best evaluation for enclosure concentration without complete mixing is the measurement of the concentration in the exhaust duct. 

Air stream A defined air current within an enclosure, resulting from natural thermal air movement or from mechanical air movement produced by a jet. 

Originally the classification of materials was derived from tests of proprietary explosion-proof (flameproof) enclosures. There were no published criteria. Equipment was approved relative to the lowest ignition temperature of any material in the group (Magison 1987). In about 1965 the U.S. Coast Guard asked the National Academy of Sciences (NAS) to form a panel to classify 200 materials of commerce. The Electrical Hazards Panel of the Committee on Hazardous Materials was formed by the NAS. The Panel studied many ways to estimate the hazard classification of materials. The Panel finally reported to die U.S. Coast Guard in 1970 that no workable, predicdve scheme could be defined, and it then proceeded to assign tentative classifications to the 200 materials. 

An open independently ventilated machine is one which is ventilated by means of a separate motor-driven blower mounted on the machine enclosure. Mechanical protection shall be as defined in 1.25.1a to 1.25.5a, inclusive. This machine is sometimes known as a blower-ventilated machine. 

The letters or letter following the type number indicates the particular groups or groups of hazardous locations (as defined by the National Electrical Code) for which the enclosure is designed. The designation is incomplete without a suffix letter or letters. 

In the enclosure rule, all paths from A back to A that use only associations defined within the box (or that do not use any links marked cross ) are guaranteed to get back to the same instance of A that is, all links lie within the tree of objects that is rooted at self A. By contrast, although a.b.x.d is certainly a member of type A, it need not be = a. 

Other kinds of electrical equipment may also be used in hazardous locations. One kind is purged and pressurized electrical equipment. This equipment works by using air or nonflammable protective gas flow or pressure to prevent hazardous materials from entering the enclosure NFPA 496 defines three types of purged and pressurized equipment as identified in Table 7-5. 

Because the useftd quantity for a refrigerator is the amount of heat that it removes from the enclosure, we define its coefficient of performance as... 

There are a large number of different methods used for bench-scale assessment of combustion toxicity, and the applicability of test data to lire hazard assessment is not always clear. Obviously, toxic potency data should not be used in isolation but should either be a part of a classification scheme or as part of the input to lire risk and lire safety engineering assessments. It is important that uncertainty or confidence limits should be used with toxic potency data, because they are often relatively large. Fire effluent toxic potency does not have a unique value but is a function of the material and the fire conditions, particularly temperature and oxygen availability in the fire zone, and also the fire environment (enclosure, geometry, and ventilation). To assess the fire hazard, toxic potency data must be relevant to the end use fire situation, and the fire condition, which can be defined using the ISO classification of fire stages. 

Explain how the computer program for the calculation of flow in a porous medium-filled vertical enclosure given in this chapter must be modified to deal with the case where the heat flux rather than the temperature at the hot wall is specified. For this purpose, define the following dimensionless temperature ... 

The emissive power of a body E is defined as the energy emitted by the body per unit area and per unit time. One may perform a thought experiment to establish a relation between the emissive power of a body and the material properties defined above. Assume that a perfectly black enclosure is available, i.e., one which absorbs all the incident radiation falling upon it, as shown schematically in Fig. 8-4. This enclosure will also emit radiation according to the T law. Let the radiant flux arriving at some area in the enclosure be q, W/m2. Now suppose that a body is placed inside the enclosure and allowed to come into temperature equilibrium with it. At equilibrium the energy absorbed by the body must be equal to the energy emitted otherwise there would... 

This parabola defines the area of flame transmission through the joint. Its vertex is usually nearby or somewhat below the stoichiometric point. All gases show a behaviour similar to that shown in Fig. 1.3. The knowledge of the vertex MESG values of gas-air or vapour-air mixtures is essential for the construction and use of enclosures, type of protection flameproof... 

Figure 2.5 The zone 2 concept according to VDE 0165/1991-02. Requirements for electrical apparatus with arcs or sparks in normal operation and/or temperatures exceeding a defined limit/temperature class. Two types of protection are defined here the schwadensicheres Gehause , comparable with a restricted breathing enclosure , and simple pressurization .

For electrical apparatus outside of this scope, e.g. switchgear, IEC 60079-15 defines a protection technique restricted breathing enclosure. ... 

Special protection comprises all protection techniques such as powder filling, static pressurization and encapsulation (by plastics materials). At that time, these techniques started their career in the field of explosion protection and advanced to autonomous types of protection described by IEC or European Standards individually. VDE 0170/0171/1969-01 does not contain any specific requirements for these techniques. It has been the decision of the certifying body that an s -apparatus will operate at the same level of safety compared with other well-defined types of protection, e.g. flameproof enclosure d ... 

TGL 30042 has defined a four-zone concept for areas hazardous due to combustible gases, vapours and mists EG 1, comparable with zone 0 EG 2 and EG 3, covering zone 1 EG 4, comparable with zone 2. In contradiction to the majority of standards covering the zone 1 requirements with all types of protection such as flameproof enclosure, increased safety, pressurization, oil immersion, intrinsic safety, powder filling, EG 2 excludes the general application of, e.g., increased safety e, which has been the domain of EG 3. 

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